1. Field of the Invention
Embodiments of the present invention relate in general to toner and developer compositions, and more specifically, to the use of one or more copolymers in the toner preparation process. According to a first aspect, one or more copolymers are combined with colorant particles which are then combined with primary toner particles to form composite toner particles which are referred to generally herein as toners. According to a second aspect, one or more copolymers are combined with primary toner particles. The combination is then combined with colorant particles to form toners. According to a third aspect, one or more copolymers are used as seed particles during preparation of a primary toner particle. According to one embodiment, the one or more copolymers are encapsulated within a primary toner particle and optionally can be uniformly distributed throughout a primary toner particle which is then used to form toners.
The resulting toners can be selected for known electrophotographic imaging and printing processes, including color processes, digital imaging, combined facsimile, copier, and printer applications and lithography.
2. Description of Related Art
Known reprographic technologies, such as xerographic and ionographic technologies and devices utilize toners having small average volume diameter particle sizes which can generally range from about 2 microns to about 20 microns. In certain xerographic applications, such as high volume copier-duplicator applications, high resolution characteristics and low image noise are highly desired. These characteristics can be readily attained utilizing small sized toners with volume average diameters of less than 11 microns, preferably between about 2 and about 7 microns, and with narrow geometric size distribution (GSD) of less than about 1.6 or preferably less than about 1.4. Additionally, in some xerographic systems wherein process color is required such as pictorial color applications, small particle size colored toners of about 2 to about 10 microns volume average diameter are highly desired to avoid paper curling which results when moisture is driven out of the paper due to high fusing temperatures of from about 120.degree. C. to about 200.degree. C. Paper curling can be particularly pronounced in xerographic color processes primarily because of the presence of relatively high toner coverage as a result of the application of three to four color toners. The size and amount of the toner particle in part dictates the amount of heat required to fuse the toner to the paper. Lower particle sizes require less heat and therefore produce less paper curling during the fusing process. The amount of toner layers present on the paper to be fused also effects paper curling since a thicker toner plastic level present after the fusing step inhibits the paper from sufficiently absorbing the moisture lost during the fusing step, and image paper curling results. These and other imaging shortfalls and problems are avoided or minimized with the toners and processes of the present invention.
Certain toner particle sizes can be selected, such as from about 2 to about 10 microns volume average diameter, and with a high colorant loading such as from about 3% to about 65% by weight of toner, or from about 3% to about 25% by weight of toner, so that the mass of toner necessary for attaining the required optical density and color gamut can be significantly reduced to eliminate or minimize paper curl. Lower toner mass also promotes image uniformity. However, higher pigment loading often adversely affects the charging behavior of toners. For example, the charge levels may be too low for proper toner development or the charge distributions may be too wide and toners of wrong charge polarity may be present. Furthermore higher colorant loadings may also result in sensitivity of charging behavior to changes in environmental conditions such as temperature and humidity. Toners prepared in accordance with the processes of the present invention minimize, or avoid these disadvantages.
Numerous processes are known for the preparation of toners, such as, for example, conventional processes wherein a resin is melt kneaded or extruded with a pigment, micronized and pulverized to provide toner particles with a volume average diameter of from about 7 microns to about 20 microns and with broad geometric size distributions. In such processes it is usually necessary to subject the aforementioned toners to a classification procedure such that the geometric size distribution of from about 1.2 to about 1.6 or from about 1.2 to about 1.4 are attained. However, in the aforementioned conventional process, low toner yields after classifications may be obtained.
Additionally, other processes such as and including encapsulation, coagulation, coalescence, suspension polymerization, or semi-suspension and the like, are known, wherein the toners are obtained by in situ one pot methods. Moreover, encapsulated toners are known wherein a core comprised of pigment and resin is encapsulated by a shell, and wherein the toner melt Theological properties are separated wherein a core material provides low fusing properties such as from about 100.degree. C. to about 125.degree. C., and an encapsulating shell provides necessary blocking properties for particle stability prior to fusing. Other in situ toners prepared by suspension, coagulation, coalescence, are known, wherein the toners are comprised of substantially similar composition to conventional toners with, in some cases, having surfactants or surface additives on the toner surface prepared by various processes.
U.S. Pat. No. 4,996,127 illustrates a toner of associated particles including primary particles of a polymer having acidic or basic polar groups and secondary particles of a coloring agent. The polymers selected for the toners of the '127 patent can be prepared by an emulsion polymerization method; see for example columns 4 and 5 of this patent. In column 7 of this '127 patent, it is indicated that the toner can be prepared by mixing the required amount of coloring agent and optional charge additive with an emulsion of the polymer having an acidic or basic polar group obtained by emulsion polymerization. U.S. Pat. No. 4,983,488 discloses a process for the preparation of toners by the polymerization of a polymerizable monomer dispersed by emulsification in the presence of a colorant and/or a magnetic powder to prepare a principal resin component and then effecting coagulation of the resulting polymerization liquid in such a manner that the particles in the liquid after coagulation have diameters suitable for a toner. This process results in, it is believed, the formulation of particles with a wide particle size distribution. Hence, classification, is required, resulting in low toner yields. U.S. Pat. No. 4,797,339 discloses a process for the preparation of toners by resin emulsion polymerization, wherein certain polar resins are selected. U.S. Pat. No. 4,558,108 discloses a copolymer of styrene and butadiene produced by specific suspension polymerization. Other prior art includes U.S. Pat. Nos. 3,674,736, 4,137,188 and 5,066,560.
Emulsion/aggregation/coalescence processes for the preparation of toners are illustrated in a number of patents, the disclosures of each of which are totally incorporated herein by reference, such as U.S. Pat. No. 5,290,654, U.S. Pat. No. 5,278,020, U.S. Pat. No. 5,308,734, U.S. Pat. No. 5,370,963, U.S. Pat. No. 5,344,738, U.S. Pat. No. 5,403,693, U.S. Pat. No. 5,418,108, U.S. Pat. No. 5,364,729, and U.S. Pat. No. 5,346,797. U.S. Pat. No. 5,853,943 discloses the preparation of a seed particle latex by aqueous emulsion polymerization of a portion of an initial monomer emulsion. The remainder of the initial monomer emulsion is then added to the seed particle latex. Also of interest may be U.S. Pat. Nos. 5,348,832, 5,405,728, 5,366,841, 5,496,676, 5,527,658, 5,585,215, 5,650,255, 5,650,266, 5,368,970, 5,486,444, 5,866,290, 5,582,951, 5,302,486, 5,223,370, 5,153,089, 5,114,819, 5,080,986, 5,045,422, 5,023,159, 5,013,630, 5,334,471, 5,346,790, 5,145,762, 5,766,817 and 5,501,935 each of which are incorporated herein by reference in their entireties. Additional patents which may be of further interest include U.S. Pat. Nos. 5,520,993, 5,573,825, 5,647,107, 5,698,296 and 5,888,622.
Accordingly, there is a need to develop processes for the manufacture of toners having small average particle sizes of from about 1 micron to about 25 microns, from about 2 microns to about 12 microns, from about 3 microns to about 9 microns and preferably from about 5 to about 7 microns without resorting to classification processes, and wherein high toner yields are attained such as from about 90 percent to about 99.7 percent or higher or from about 92 to about 96 percent, and ranges in between, in certain embodiments.
There is a further need to develop processes for the manufacture of toners where colorants are uniformly dispersed throughout a toner particle or portions of a toner particle. There is a still further need to develop processes for the manufacture of toners having improved charging and fusing (crease) properties, projection efficiency and toner color properties. Lower fusing temperatures reduce the energy requirements of the fuser and more importantly result in lower moisture driven off from the paper during fusing, and hence lower or minimize paper curling. There is an even still further need to develop toners having improved mechanical properties by the inclusion of components such as copolymers which reinforce the structure of the toners.
There is an even still further need to develop toners having useful glass transition temperatures, and that are suitably resistant to caking, blocking or undesired aggregation of toner particles, and further having suitably low fixing temperatures as well as useful triboelectric, gloss and humidity characteristics.
There is a need for black or colored toners wherein small particle sizes of less than or equal to 25 microns in volume diameter, and preferably between about 1 micron and about 25 microns, between about 2 microns and about 20 microns, between about 3 microns and about 9 microns, or between about 5 microns to about 7 microns in volume diameter.